We've looked all over the place for hard numbers and didn't yet come up with a number higher than 5 CURRENTLY.

According to The Daily Climate:

Every day, 20 freight trains rumble through downtown Billings. Five of those are coal trains – 120 cars stretching a half-mile and carrying 17,000 tons of coal west.

The trains bisect the town, cutting affluent north from poorer and predominantly minority south. The city's only two hospitals sit on the northern half of town, and residents fear that one day a long wait – or a train wreck – could leave a large chunk of the city isolated from medical care.

Sounds plausible although we were unable to find an example of that scenario happening YET. Either way, the number of trains loaded with coal does seem to be on the rise and there's no reason to think it would decline.